1. Field of the Invention
The present invention relates to a pressurization system for pressurizing a liquid holding tank on a truck such as a water truck of the type generally used to clean and/or keep road surfaces damp to minimize dust in construction operations and the like. Such trucks can also be used as a source of water under pressure for fire fighting, etc. More particularly, the present invention relates to such a truck with a chassis mounted water tank which is pressurized via the engine exhaust of the truck.
2. Description of the Related Art
Trucks which carry water tanks for spraying water on road surfaces and the like are well known. Many such trucks simply employ a bottom mounted discharge with a gravity feed system for emptying the tanks. However, in order for the water to be used for cleaning road surfaces, fighting fires, or simply pumping water to a higher elevation, such water trucks must employ a pressurization system for the water tank.
Heretofore, many water trucks employed discharge systems with positive-displacement pumps fluidically communicating with their water tanks for discharging the contents thereof under pressure. Such a water discharge pump can be driven by a respective vehicle engine through a power take-off (PTO) unit. Alternatively, a "pony" motor, comprising a suitable internal combustion engine, can be mounted on the vehicle for operating the water pump or pumps independently of the vehicle's engine.
A significant problem with previous water trucks relates to problems associated with freezing of the water contents. Positive displacement pumps, such as those used with previous water trucks, may be particularly susceptible to damage caused by the freezing of water left therein. Such freeze-damage to a water pump can cause downtime for the water truck and necessitate the repair or replacement of the damaged water pump at considerable expense, particularly since these types of pumps can be relatively expensive and/or time consuming to repair or replace. Moreover, if delays are encountered in obtaining a replacement pump or parts therefor, the downtime for the water truck can substantially increase.
Protecting previous water trucks from freeze damage often involved blowing out their water systems with pressurized air, draining their contents with appropriate petcocks, etc. Previous water trucks with pumps driven by PTO's and pony motors thus tended to be relatively complex and required time-consuming winterization procedures for protection when subjected to temperatures below freezing.
Another disadvantage with a PTO-driven pump is that its output is dependent upon the speed of the vehicle engine. The optimum engine speed for a PTO-driven pump can be at or near idle, but operating the vehicle over various road conditions in different gears can cause wide fluctuations in pump output with resulting uneven water distribution.
Still further, PTO drive systems and pony engines can add considerably to both the initial cost and the ongoing maintenance expenses associated with a water truck. Such previous trucks and their water distribution systems also tended to have a number of moving parts, which were susceptible to damage and wear from freezing and other causes.
It is therefore preferable to provide a water distribution system wherein the water tank is pressurized as needed with relatively few moving parts and with a relatively simple freeze protection system. Moreover, it is preferable to provide a water distribution system which can operate at engine idle speed yet provide reliable pressurization for attaining operating pressures of up to 35 PSI, and to provide such a system which can accommodate various water application procedures such as dust control, fire fighting, etc.
Heretofore there has not been available a water truck with a pressurized discharge system having the advantages and features of the present invention.